Feature/add dependabot and codeql security checks (#4479)

* Add CodeQL analysis workflow configuration

* Add Dependabot configuration for package updates

Configure Dependabot to check for updates in various ecosystems weekly.

* Fix dependabot.yml: bun ecosystem, missing dir, grouping for PR #4479

1. studio/frontend uses bun.lock not package-lock.json, so change npm to bun
2. Add missing studio/backend/requirements/ pip entry (consumed by studio/setup.sh)
3. Add groups with patterns ["*"] to all pip/bun/npm entries to batch updates
   and avoid 30+ individual Dependabot PRs on the first run

* Consolidate pip blocks to fix overlapping directory violation

GitHub Dependabot forbids multiple same-ecosystem entries with
overlapping directories on the same branch. The root "/" directory
overlapped the 3 nested pip dirs. Merge all 4 pip blocks into one
using the `directories:` (plural) key.

Also remove redundant open-pull-requests-limit from the bun block
since grouping with patterns: ["*"] already limits PR count.

---------

Co-authored-by: Daniel Han <danielhanchen@users.noreply.github.com>

.github/workflows/codeql.yml

@@ -0,0 +1,46 @@
+---
+name: "CodeQL"
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+  schedule:
+    - cron: "25 14 * * 3"
+  workflow_dispatch:
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      packages: read
+      actions: read
+      contents: read
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: python
+            build-mode: none
+          - language: javascript-typescript
+            build-mode: none
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v3
+        with:
+          category: "/language:${{ matrix.language }}"
+...